Gamma radiation nitration of alkanes



United States Patent ()fihce arrears Patented Feb. 4, 1964 3,120,478 GAMMA RADIATION NIIRATION 6F ALKANES Lyie F. Albright, Lafayette, and Roberto Lee, West Lafayette, ind, assignors to Purdue Research Foundation, West Lafayette, Ind, a corporation of Hndiana No Drawing. Filed Get. 6, 1960, Ser. No. 60,789 6 Claims. (Cl. 204-162) This invention relates to the nitration of saturated aliphatic hydrocarbons. More particularly, it pertains to the production of nitroalkanes by the vapor phase nitration of saturated aliphatic hydrocarbons of the paraflin series at elevated temperatures by means of nitric acid, oxides of nitrogen, and the like, in the presence of regulated amounts of oxygen and gamma radiation.

Numerous efforts have been made in the past to develop a satisfactor method of obtaining nitroallran'es. The most effective previously disclosed processes are those of Hass et al. described in U.S. Patent Nos. 1,967,667, 2,071,122 and 2,206,813, pertaining to the vapor phase nitration of paraflin hydrocarbons such as ethane, propane, butane, and the like, by means of nitric acid or nitrogen dioxide; the process or" Landon, described in U.S. Patent No. 2,161,475 pertaining to the nitration of methane by means of nitric acid; and that-of Hass et al., described in U.S. Patent No. 2,609,401, pertaining to the use of oxygen in the vapor phase nitration of alkanes.

All of the prior art processes are open to a number of serious objections, one of the most important of which has been the low conversions and yields of products obtained based on the nitric acid used in the process. 'Because of its cost, corrosiveness, and the like, it is highly desirable to use as small a quantity of nitric acid as possible. We have now discovered that the conversion of nitric acid to nitroalkanes as well as the production of valuable oxidation products when paraffin hydrocarbons are nitrated in the vapor phase can be materially increased by effecting the vapor phase nitration of the hydrocarbons in the presence of oxygen and under the effects of gamma radiation in regulated amounts under certain restricted conditions of time and temperature. This is accomplished by having the vapor phase nitration reaction in the presence of gamma radiation.

The improved process whereby we obtain increased conversions and yields of both nitroalkanes and oxidation products such as alcohols, aldehydes, acids, etc, involves conducting the vapor phase nitration of saturated aliphatic hydrocarbons with a nitrating agent such as nitric acid in the presence of oxygen. The hydrocarbon of our process is used in an amount of about ten mols per mol of nitrating agent and the oxygen in concentrations that do not produce explosive mixtures, preferably in equal mol ratios to the nitrating agent. The nitration reaction chamber is irradiated by gamma radiation of the intensity of at least about 200,000 roentgens per hour. By carrying out the nitration under such conditions the conversions to nitroalkanes, based on nitric acid, are increased substantially over the conventional method of nitration in the absence of gamma radiation. Such increases in conversions and yields permit the production of nitroalkanes at materially lower costs because of increases in plant capacity, lower raw material costs, and lower labor costs. it is obvious that even relatively low increases in conversions are of great importance in the production of relativel expensive materials such as the nitroalkanes.

Our process is, in general, applicable to the nitration of saturated aliphatic hydrocarbons containing from 1 to 4 carbon atoms such as methane, ethane, propane, butane and isobutane.

Our process may be satisfactorily carried out over a wide temperature range, from about 370 C. to about 460 C., depending upon the hydrocarbon being nitrated, the products desired, and other process conditions. However, the reaction time must be altered in accordance with the temperature used, substantially longer time being required for the lower temperatures. In general, the higher the temperature employed, the shorter will be the contact time for optimum conversion of nitric acid to nitroalkanes. The contact times used when the reaction is carried out under gamma radiation do not differ substantially from those used in nitrations carried out in the absence of gamma radiation. Accordingly, in carrying out our improved process the temperatures, reaction times, and space velocity are regulated in the same general manner as in the prior art processes. The source of gamma radiation can be any convenient source such as sodium-22, aluminum-26, potassium-40, cobalt-60, columbium-94, lanthanum-138, and bismuth-207. Sources other than the above named radioactive isotopes can also be used for irradiation with gamma rays.

Both nitric acid vapors and nitrogen dioxide may be used as nitration agents in our process, although we prefer to use nitric acid vapors. In general, the conditions for using nitrogen dioxide in our process are the same as those employed in the unradiated nitrations. However, the conversions of nitrogen dioxide to ni-troalkanes are somewhat lower than those obtained with nitric acid under respective optimum conditions.

Normally, the contact time and radiation time will be essentially the same for our reaction. This is because it is most convenient to have our reaction chamber within the container of the radioactive material or in proximity to the radioactive material so that a high level of gamma radiation will enter the reaction chamber. Therefore the radiation exposure and contact time will be essentially the same and will normally be only when the reactants are in the reactor. The optimum time of contact for a given reaction temperature can almost immediately be determined for a given reaction mixture by regulating the time of contact for the reaction mixture at the selected reaction temperature so as to maintain the acidity of the reaction products within a relatively narrow range. Since water is one of the reaction products of the nitration reaction, the nitroalkanes are in all cases at least partially immiscible with water, the liquid reaction products separate into two layers. The titratable acidity of the aqueous layer constitutes a convenient measure of the acidity of the reaction products, and this value may be used as a :basis for the control of the time-temperature factor. Increase in acidity above the desired range would necessitate reaction temperature increases or contact time increases or both. Similarly, acidity below desired operating range, would necessitate temperature decreases, or contact time decreases, or both. The acidity of the aqueous layer of the product should be maintained within the range of 0.1 N to 1.5 N in order to obtain best results. U.S. Patent No. 2,609,401 by Hass et a1. and U .S. Patent No. 2,327,964 by Hodge more completely discloses the relationship of the reaction time and acidity of the aqueous layer of the product.

As previously indicated, our process gives rise to increased conversions of nitroalkanes and also to increased formation of oxidation products of the hydrocarbon being used.

Our process will be illustrated by the following examples:

Example I A reaction mixture consisting of 5.10 gram mols of propane per hour, 0.523 gram mols of nitric acid per hour, 0.845 gram mols of water per hour, and 0.49 gram mols of oxygen per hour was passed in the vapor phase through a reactor constructed from glass tubing of about 1.0 inch outer diameter and 13.5 inches in length, having a volume of about 117.1 milliliters, at an average temperature of about 380 C., under a pressure of 770 millimeters Hg, at a contact time of 1.06 seconds. The conversion of nitric acid to nitroalkanes was 25.8 percent. This reaction was repeated with the exception that the reactor used was exposed to a gamma radiation source which had an exposure dose rate of 195,000 roentgens per hour from an 800 curie cobalt-60 source. The reaction under the exposure of gamma radiation gave a 45.7 percent conversion of nitric acid to nitroalkanes. This is a 77 percent increase in the conversion rate.

Example 11 A reaction mixture consisting oi 5.10 gram mols of propane per hour, 0.55 gram mol of nitric acid per hour, 0.741 gram mol of Water per hour, and 0.49 gram mol oxygen per hour was passed in the vapor phase through a reactor constructed from glass tubing of about 1.0 inch outer diameter and 13.5 inches in length, having a volume of about 117.1 milliliters, at a temperature of about 425 C., under pressure of 770 millimeters Hg, at a contact time of 1.06 seconds. The conversion of nitric acid to nitroalkanes wa 36.3 percent. This reaction was repeated with the exception that the reactor used was exposed to a gamma radiation source which had an exposure dose rate of 195,000 roentgens per hour from an 800 curie cobalt- 60 source. The reaction under the exposure of the gamma radiation gave a 47.3 percent conversion of nitric acid to nitroalkanes. This is a 30 percent increase in the conversion rate.

It is to be understood, of course, that we are not limited to the specific operating procedures set forth in the above specific examples since various modifications of the procedures set forth therein will naturally occur to those skilled in the art.

Now having disclosed our invention, what we claim is:

1. A process for producing nitroalk-anes which comprises contacting a low-e alkane with a nitratin agent and oxygen in the vapor phase at temperatures ranging from about 370 C. to about 460 C. in the presence of gamma radiation with the proviso that oxygen is present in nonexplosive concentrations and the gamma radiation is maintained at an intensity of not less than 200,000 roentgens per hour.

2. The process of claim 1 wherein the nitrating agent is nitric acid.

3. The process of claim 1 wherein the mole ratio of lower alkane to nitrating agent is about 10 to 1 respective- 1y.

4. A process for producing lower nitroalkanes which comprises contacting a lower alkane having from 1 to 4 carbon atoms with nitric acid and oxygen in the vapor phase at temperatures ranging from about 370 C. to about 460 C. in the presence of radiation with the provisos that oxygen is present in non-explosive concentrations and the gamma radiation is maintained at an intensity of not less than 200,000 roentgens per hour, the time of the reaction being regulated so that the acidity of the aqueous reaction products is maintained at a substantially constant value between 0.1 N to 1.5 N.

5. The process of claim 4 wherein the lower alkane is propane.

6. The process of claim 4 wherein the source of gamma radiation is cobalt-60.

References Cited in the file of this patent UNITED STATES PATENTS 2,609,401 Hass et al Sept. 2, 1952 FOREIGN PATENTS 665,263 Great Britain Ian. 23, 1952 OTHER REFERENCES Charlesby: Atomic Radiation and Polymers, 1960, page 182. 

1. A PROCESS FOR PRODUCING NITROALKANES WHICH COMPRISES CONTRACTING A LOWER ALKANE WITH A NITRATING AGENT AND OXYGEN IN THE VAPOR PHASE AT TEMPERATURES RANGING FROM ABOUT 370*C. TO ABOUT 460*C. IN THE PRESENCE OF GAMMA RADIATION WITH THE PROVISO THAT OXYGEN IS PRESENT IN NONEXPLOSIVE CONCENTRATIONS AND THE GAMMA RADIATION IS MAINTAINED AT AN INTENSITY OF NOT LESS THAN 200,000 ROENTGENS PER HOUR. 